It is often necessary to shift the voltage range of a signal from a low voltage range, such as a logic level of 0 to 1.1 volts, as often used in the core of processor integrated circuits, or 0 to 3.3 volts, as often used in the periphery of processor integrated circuits, to a higher voltage range. For example, a higher voltage range of 0 to 5 volts is commonly used in digital integrated circuits and these circuits may have low voltage cores. Mixed-signal integrated circuits, such as an integrated circuit for use in power handling and display driving circuitry, often must handle high voltages while often requiring considerable low voltage logic circuitry. Examples of mixed-signal circuits include microprocessor-controlled buck-type MPPT charge-controllers used to regulate solar panels, where charging a 24-volt battery may require switching peak 40-volt panel outputs; and serial-network interfaced, reversible, door-mounted, window-or-lock motor controller circuits in automobiles may also be subjected to surge voltages rising well above nominal 12-volt motor supply voltages. These are just examples, many thousands of applications exist for integrated circuits that control, switch, or sense voltages higher than their logic core voltages throughout the electronics industry; even where high currents are handled in separate discrete transistors it can be desirable for controlling integrated circuits to provide high-voltage output signals instead of requiring predrivers built of discrete components.
Switching or sensing high voltages typically requires the use of one or more high-voltage transistors in a logic level-shifter circuit integrated on the integrated circuit.
High voltage transistors integrated on conventional CMOS processes often require greater area than required for low voltage transistors on the same process. This is partly a consequence of greater source-drain channel-lengths being required at diffusions to avoid source-drain punchthrough at high voltage, relative to channel lengths required for low voltage transistors. It is also a consequence of space required for process and layout techniques required to overcome other effects including channel formation under interconnect metallization. Additional space may also be required for guardrings and similar structures intended to prevent latchup.
Gate-to-source voltage (VGS) may be limited to a maximum (VGSmax), a process-dependent value between 5 v and 20 v in some CMOS integrated-circuit processes, because exceeding this value could cause irreversible breakdown of thin gate oxides as well as punchthrough currents. Limited VGSmax restricts circuitry design in level shifters. Some process techniques exist for providing high-voltage transistors with greater VGSmax, although use of these techniques comes at a cost of increased area and decreased source-drain current per unit area, often requiring greater die area for such high-voltage transistors.